Technical Field
The present invention relates to an optical scanning unit and an image forming apparatus, and more particularly to, an optical scanning unit that scans a scanned surface, and an image forming apparatus employing the optical scanning unit.
Background Art
When recording images, Image forming apparatuses using electrophotography typically include, for example, an optical scanning unit that scans a surface of a photoconductive drum using a laser beam to form a latent image on the surface of the photoconductive drum.
The optical scanning unit includes, for example, a light source, a pre-deflector optical system, a rotatable multi-faceted mirror, and a scanning optical system. The laser beam emitted from the light source strikes the rotatable multi-faceted mirror via the pre-deflector optical system, is deflected at the reflection face of the rotatable multi-faceted mirror, and is then guided to the photoconductive drum through the scanning optical system. The reflection face of the rotatable multi-faceted mirror is also referred to as the deflective reflection face.
The laser beam can be directed to the multi-faceted mirror using an underfilled (UF) type system or an overfilled (OF) type system.
JP-2005-92129-A discloses a UF type system, in which the incident light is narrower than a length of the deflective reflection face extending along a direction corresponding to the main scanning direction, and all the incident light is reflected at the deflective reflection face.
By contrast, JP-H10-206778-A discloses a OF type system, in which the incident light is wider than a length of the deflective reflection face extending along a direction corresponding to the main scanning direction, and the periphery of the incident light does not strike the deflective reflection face.
Image forming apparatuses are increasingly expected to operate at ever-faster speeds and provide enhanced quality images. However, with conventional image forming apparatuses, it is difficult to enhance image forming speed and image quality without increasing the size and cost of the apparatus.